E-Machines eMachines Desktop PC "navigator staying end" Questions

My Girlfriends Compaq Presario sr1920nx has lots of problems... the one right now is the display. I replaced her monitor with another used one because it died. Now the one I just put on won't stay on,

windows xp desktop boot problem i have to boot several times to get pc on. makes a clicking noise some times. black and white screen appears with disk and all kinds of disc information. after i ...